Pneumatic machine for the creation of mechanical shocks of variable amplitude and intensity

ABSTRACT

The machine comprises a moving system consisting of a hollow cylinder which supports the sample to be tested and has two separate internal chambers which vary in volume in a complementary manner according to the position of a piston within the cylinder. A fixed body which guides the moving system in translation comprises an internal jacket against which bears an external collar of the cylinder, thus forming two chambers which are external to the cylinder and vary in volume with the movement of the moving system. Means are provided for applying different pressures of a pneumatic control fluid to the internal and external chambers and for abruptly varying the pressure in one of the external chambers in order to cause rapid displacement of the moving system.

United States Patent 1 Pascquet 3,750,457 Aug. 7, 1973 PNEUMATIC MACHINE FOR THE CREATION OF MECHANICAL SHOCKS OF VARIABLE AMPLITUDE AND INTENSITY [75] Inventor: Adrien Pascquet, Toulon, France [73] Assignee: Commissariat A LEnergie Atomique, Paris, France [22] Filed: Dec. 1, 1971 [21] Appl. No.: 203,638

[52] U.S. Cl. 73/12 [51] Int. Cl. G01n 3/30 [58] Field of Search 73/12 [56] References Cited UNITED STATES PATENTS 3,360,979 l/l968 Jensen 73/12 3,485,083 12/1969 Gray 73/12 Primary Examiner-Charles A. Ruehl iftorney-William B. Kerkam, Jr.

[57] ABSTRACT The machine comprises a moving system consisting of a hollow cylinder which supports the sample to be tested and has two separate internal chambers which vary in volume in a complementary manner according to the position of a piston within the cylinder.

A fixed body which guides the moving system in translation comprises an internal jacket against which bears an external collar of the cylinder, thus forming two chambers which are external to the cylinder and vary in volume with the movement of the moving system.

Means are provided for applying different pressures of a pneumatic control fluid to the internal and external chambers and for abruptly varying the pressure in one of the external chambers in order to cause rapid displacement of the moving system.

8 Claims, 2 Drawing Figures PATENTED MI? 7 i975 SHEU 2 UP 2 FIG. 2

PNEUMATIC MACHINE FOR THE CREATION OF MECHANICAL SHOCKS F VARIABLE AMPLITUDE AND INTENSITY The present invention relates to a pneumatic machine intended for the generation of mechanical shocks on a sample or specimen undergoing tests; the shocks created may have variable amplitude and intensity and may especially have a saw-tooth profile with a very steep initial peak or acceleration front followed by a slow deceleration, rectilinear if so desired, or even a more complex profile, rectangular, trapezoidal, semisinusoidal.

Shock machines are already known which are generally constituted by a plate carrying the sample to be tested, guided by one or more vertical pillars and falling with a free drop or following any other law of acceleration on to an anvil known as a impactor, the form of which is appropriate to the profile of the shock to be produced. The impactors generally employed may be made from a suitable elastic material, may have a hydraulic or pneumatic compression, or alternatively they may be subjected to plastic deformation.

These known machines have however a number of disadvantages: in particular, they necessitate a large falling travel resulting in excessive overall size. On the other hand, thesample itself cannot have too-large dimensions, the upper part of the supporting plate not being completely left free by the guiding pillars. Finally, these machines are a source of large transverse reactions when the center of gravity of the moving portion is not located strictly on the axis of this portion. For these various reasons, the conventional machines do not readily lend themselves to the production of variable shock profiles, especially of saw-tooth form with a very steep initial front, simulating an air or submarine shock wave, or an impact on materials of variable hardness such as concrete, flooring, water.

The present invention relates to a pneumatic machine which overcomes these drawbacks. To this end, this machine comprises a moving system constituted by a hollow cylinder, one end of which forms a Supporting plate for a sample to be tested, while the other end is traversed by the rod of a piston sliding in the cylinder and defining two separate internal chambers, the volumes of which vary in a complementary manner following the position of the piston in the cylinder, is characterized in that it comprises a fixed body guiding the moving system in translation and comprising a stop abutment for the extremity of the piston rod, this fixed body comprising an internal jacket coaxial and external to the cylinder, against which bears a transverse collar formed in the outer surface of this cylinder, this collar delimiting with the fixed body and the jacket two chambers external to the cylinder, the volume of which varies with the displacement of the moving system, means for putting the internal and external chambers under different pressures from a pneumatic control fluid, and means for abruptly varying the pressure in one of the external chambers in order to cause a rapid displace ment of the moving system.

In one preferred form of embodiment of the invention, the sliding piston comprises calibrated orifices which put the two internal chambers of the hollow cylinder into communication on each side of this piston.

In other alternative forms, the communication orifices formed through the sliding piston may have an adjustable section or may even be closed.

Other characteristics of a machine built in accordance with the invention will be brought out in the description which follows of an example of construction, given by way of indication and not in any limitative sense, with reference to FIG. 1 of the accompanying drawing which illustrates a view of a machine of this kind in longitudinal section and FIG. 2 which is similar to FIG. 1 and showing a modification thereof.

As can be seen from FIG. I, the machine considered mainly comprises a fixed body 1 formed by a lateral shell 2 of substantially cylindrical general shape, closed at its upper and lower extremities by two plates 3 and 4 secured to the fixed body by means of connection screws such as 5. The upper plate 3 is provided at its center with a bore 6, permitting a hollow cylinder 7 to slide freely laterally inside the fixed body.

This hollow cylinder 7 is composed of a cylindrical sheath 8, closed at its upper and lower portions by two ends 9 and 10 respectively, screwed on to threaded portions 11 and 12 of the sheath 8. Sealing joints 13 and 14 permit the completion of the assembly of the various parts of the hollow cylinder, so as to render the latter normally fluid-tight with respect to the exterior.

The guiding of the cylinder 7 with respect to the body 6 is effected by means of bearings, one of which is formed by the edge of the bore 6 and isprovided with a sliding joint 15, while the second, shown at 16 in the drawing, also comprises a sliding joint identical with that previously mentioned.

In accordance with the invention, the hollow cylinder 7 is associated with a sliding piston 18 mounted inside this cylinder, this piston 18 comprising on the one hand a head 19 provided in its outer surface with a toric joint 20 intended to provide a fluid-tight separation between two chambers of the space comprised in the interior of the sheath 8 between the extremities 9 and 10, and on the other hand, a rod 21, passing through the extremity 10 of this hollow cylinder through a bore 22 comprising a sealing joint 23.

The lower extremity 24 of the rod 21 of the sliding piston is arranged in such manner as to cooperate with a projecting collar 25 formed in the plate 4, this collar playing the part of a fixed stop for the piston rod during the course of the displacement of the cylinder 7. The piston 18 thus separates the internal space of the hollow cylinder 7 into two adjacent chambers 26 and 27 respectively, the volumes of which vary in a complementary manner following the relative displacement of the piston 18 with respect to the cylinder.

Finally, and in the example of construction shown in the drawing, passage orifices 28 provide a communication between the chamber 26 and the chamber 27, the volume of the first remaining however always substantially less than the volume of the second. It should be noted that in other alternative forms and as will be explained later, the calibrated orifices 28 may be formed in such manner as to have a section which can be varied at will or which alternatively may be partlyor wholly closed as by inserts 41' having axial ducts 42 of reduced diameter (FIG. 2).

At the exterior of the hollow cylinder 7, the fixed body 1 comprises a jacket 29 arranged coaxially to the hollow cylinder, this jacket 29 being fixed by a threaded portion 30 on the internal surface of the shell 2, so as to delimit with this latter a cavity 31 which facilitates the launching of the moving system of the machine, constituted by the hollow cylinder 7 and the sliding piston 8 which it comprises. In the outer surface of the sheath 8 is provided a transverse collar 32 provided with sliding joint 33 adapted to bear against the internal surface of the coaxial jacket 29, this collar 32, forming between itself, the outer surface of the sheath 8, the jacket 29 and the shell 2, two further chambers 34 and 35, separated from each other in a fluid-tight manner and arranged at the exterior of the hollow cylinder 7, in opposition to the chambers 26 and 27 located inside this cylinder.

The chamber 34 is coupled by a conduit 36 passing through the shell 2 to a valve 37 permitting the operation and control of the introduction into this chamber of a given quantity of a gaseous control fluid under pressure. Similarly, the chamber 35 and the cavity 31 which communicates with this chamber above the upper portion of the jacket 29 are joined by a conduit 38 to a valve 39 also enabling an appropriate fluid pressure to be created in this chamber and this cavity.

Finally, the outer chamber 34 communicates with the inner chamber 27 of the hollow cylinder 7 through the intermediary of a hole 40 of very small diameter; this chamber 34 can be abruptly put into communication with the external atmosphere by a rapid opening valve 41 having a large section of passage.

The operation of the shock machine described above is then as follows:

The valve 41 being closed, the chamber 26 and 27 on the one hand and 34 on the other are put under pressure by the control fluid, brought into the chamber 34 through the conduit 36 and the valve 37, this fluid filling the chambers 26 and 27 by means of the communication hole 40 and the orifices 28. The pressure in the chambers 26, 27 and 34 is thus brought up to a given value equal to P,,.

At the same time, the chamber 35 and the cavity 31 which communicates with this latter are filled with the same control fluid through the conduit 38 and the valve 39, the pressure in this case being brought to a value P,, lower than P,. Under these conditions and due to the excess of the pressure P, in the chamber 34 with respect to the pressure P, in the chamber 35, the hollow cylinder 7 becomes pushed towards the top of the drawing, the collar 32 coming into abutment against the lower face of the plate 3 closing the fixed body 1.

Similarly, the piston 8 is forced against the bottom of the hollow cylinder by the pressure P, which exists in the chamber 27 and which is applied over the whole surface of the head 19 of the piston, while this same pressure is applied in the chamber 26 only against a smaller surface, reduced by the section of the rod 21.

The machine being thus ready for working, there is arranged on the upper face of the bottom 9 of the hollow cylinder 7 a sample A to be tested, which can be directly fixed on this bottom or alternatively may be carried by a support (not shown) which is in turn fixed with respectto the cylinder.

in the following phase, the chamber 34 is very rapidly scavenged by abruptly opening the valve 41. The pressure P, which is then applied against the upper face of the collar 32 provided in the outer surface of the sheet 8, acts on the hollow cylinder and immediately drives it downwards with a rapid movement at a speed V, with respect to the fixed body 1. It should be noted that the very small diameter of the hole 40 does not permit the pressure in the chamber 34 to be equalized sufficiently quickly with that of the pressure P, which exists in the chamber 27.

The downward movement of the hollow cylinder 7 thus continuing under the above conditions, the rod 21 of the piston 18 comes at a given moment into contact with the collar 25 of the lower plate 4 ofthe fixed body 1 which forms a stop abutment for that rod. By inertia, the hollow cylinder 7 and in consequence the sample A carried on its upper extremity 9, continue their movement, causing the volume of the chamber 26 to increase, with a corresponding decrease in that of the chamber 27.

The communication orifices 28, pierced through the head 19 of the piston 18 then enable the control fluid contained in the chamber 27 to progressively fill the chamber 26 while creating therein an increasing pressure P,,. This pressure P',,, by being applied against the lower extremity 10 of the hollow cylinder with a surface S, less than the section S of the head 19 in the chamber 27, gives rise to a force P',,S' which is deducted from the substantially constant force P,,S acting on the upper extremity 9.

For this reason, the resultant force P,,S P,,S' decreases and produces on the moving system a deceleration equal to:

in which M is'the sum of the masses of the hollow cylinder 7 with its upper extremity 9 supporting the sample A and its lower extremity l0, and of the piston 18. The speed of the assembly falls until it becomes zero and even reverses sign.

The acceleration thus given to the sample A has a saw-tooth profile with an initial peak. From then onwards, due to a suitable choice of the pressure P, and P,, this initial peak may have a front with a very steep slope; in addition, for a suitable diameter of the orifices 28 pierced through the head 19 of the piston 18, this profile may correspond, after the initial peak, to a substantially rectilinear descent.

it should be noted that the force which creates the acceleration becomes reversed in all cases when the head 19 of the piston 18 is no longer applied against the extremity 10 of the cylinder, that is to say when the extremity 24 of the rod 21 becomes applied against the collar 25 of the plate 4 forming an abutment. The duration of the rising front of the profile of the acceleration is thus also a function of the rigidity of these abutments.

In addition, it is found that the maximum level of acceleration can be regulated simply by varying the value of the pressure P,,, while the duration of the profile is adjusted by varying the pressure P,.

By virtue of these arrangements, the machine according to the invention makes it possible, if so desired, to obtain complex shock profiles, especially rectangular, or trapezoidal in particular, by partially or totally closing the orifices pierced through the head of the moving piston. Similarly, a semi-sinusoidal profile may be obtained by interposing an elastic spring 40 (FIG. 2) between the extremity of the piston rod and the collar of the fixed body forming an abutment.

As will already result from the foregoing description, it will be understood that the invention is not limited to the single example of construction which has more particularly been described above; on the contrary, it embraces all alternative forms. In particular, it is possible to utilize only the moving system associated with the sliding piston as a programming device for saw-tooth shocks with an initial peak for impact machines which at present exist. Similarly, it will be observed that no condition is imposed with respect to the particular position of the machine concerned, which could be placed either vertically or horizontally, and could operate in this second case as a shock programming device on a horizontal catapult.

Irrespective of the method of application considered, the machine offers very many advantages: due to the fact that no elastically or plastically-deformed part is utilized, the number of shocks possible is practically unlimited. The guiding of the moving system with respect to the fixed body readily enables the sample and the whole of the load to be slightly off-centered without fear of transverse reactions. The launching travel of the moving system'is relatively small; on the other hand, the upper space left free for placing the sample in position is completely liberated. Finally, the speed of impact is as low as possible for a given shock, the speed of the moving system changing in direction during the actual shock for an asymmetric profile such as a sawtooth with an initial peak.

The machine in question can finally be employed for numerous tests or experiments, especially for tests on materials of any kind, the saw-tooth profile having especially the advantage of giving a constant damage potential over a very wide range of frequencies, greater than that of saw-tooth profiles with a final peak or semi-sinusoidal. In addition, the machine according to the invention makes it possible to simulate, under very closely related conditions, real shocks to which the ma terials tested may be subjected.

What we claim is:

l. A pneumatic machine for the creation of mechanical shocks having variable amplitude and intensity, comprising a moving system constituted by a hollow cylinder of which one extremity forms a supporting plate for a sample to be tested while the other extremity is traversed by the rod of a piston sliding in the cylinder and defining two separate internal chambers, the volumes of which vary in a complementary manner according to the position of the piston in the cylinder, and

wherein said machine comprises a fixed body guiding the moving system in translation and comprising a stop abutment for the extremity of the piston rod, said fixed body comprising an internal jacket coaxial and external to the cylinder, against which bears a transverse collar provided in the outer surface of said cylinder, said collar delimiting with the fixed body and the jacket two chambers external to the cylinder, the volume of said chambers varying with the movement of the moving system, means for applying different pressures of a pneumatic control fluid to the internal and external chambers, and means for abruptly varying the pressure in one of the external chambers in order to cause rapid displacement of said moving system.

2. A machine as claimed in claim 1, wherein the sliding piston comprises calibrated orifices putting the two internal chambers of said hollow cylinder into communication on each side of said piston.

3. A machine as claimed in claim 1, wherein the communication orifices formed through the sliding piston have an adjustable section or are partly or wholly closed.

4. A machine as claimed in claim 1, wherein the ho]- low cylinder is guided in lateral movement by bearings carried by the internal surface of the fixed body.

5. A machine as claimed in claim 1, wherein one of the chambers external to said cylinder communicates with one of the internal chambers by means of a hole of very small diameter formed in the surface of said hollow cylinder.

6. A machine as claimed in claim 5, wherein said means for abruptly varying the pressure in said external chamber communicating with the internal chamber includes a valve with rapid opening and a large section of passage communicating with the external atmosphere.

7. A machine as claimed in claim 1, wherein the internal chamber traversed by the sliding piston rod has a volume substantially less than that of the other internal chamber.

8. A machine as claimed in claim 1, wherein an elastic spring is mounted between said sliding piston and the stop abutment carried by the fixed body. 

1. A pneumatic machine for the creation of mechanical shocks having variable amplitude and intensity, comprising a moving system constituted by a hollow cylinder of which one extremity forms a supporting plate for a sample to be tested while the other extremity is traversed by the rod of a piston sliding in the cylinder and defining two separate internal chambers, the volumes of which vary in a complementary manner according to the position of the piston in the cylinder, and wherein said machine comprises a fixed body guiding the moving system in translation and comprising a stop abutment for the extremity of the piston rod, said fixed body comprising an internal jacket coaxial and external to the cylinder, against which bears a transverse collar provided in the outer surface of said cylinder, said collar delimiting with the fixed body and the jacket two chambers external to the cylinder, the volume of said chambers varying with the movement of the moving system, means for applying different pressures of a pneumatic control fluid to the internal and external chambers, and means for abruptly varying the pressure in one of the external chambers in order to cause rapid displacement of said moving system.
 2. A machine as claimed in claim 1, wherein the sliding piston comprises calibrated orifices putting the two internal chambers of said hollow cylinder into communication on each side of said piston.
 3. A machine as claimed in claim 1, wherein the communication orifices formed through the sliding piston have an adjustable section or are partly or wholly closed.
 4. A machine as claimed in claim 1, wherein the hollow cylinder is guided in lateral movement by bearings carried by the internal surface of the fixed body.
 5. A machine as claimed in claim 1, wherein one of the chambers external to said cylinder communicates with one of the internal chambers by means of a hole of very small diameter formed in the surface of said hollow cylinder.
 6. A machine as claimed in claim 5, wherein said means for abruptly varying the pressure in said external chamber communicating with the internal chamber includes a valve with rapid opening and a large section of passage communicating with the external atmosphere.
 7. A machine as claimed in claim 1, wherein the internal chamber traversed by the sliding piston rod has a volume substantially less than that of the other internal chamber.
 8. A machine as claimed in claim 1, wherein an elastic spring is mounted between said sliding piston and the stop abutment carried by the fixed body. 